A standard four-high rolling stand of the type used for rolling strip steel and described in German patent document No. 3,331,055 has a pair of vertically spaced nip-defining working rolls of relatively small diameter and typically of bottle shape. Respective upper and lower backup rolls of larger diameter bear respectively down and up toward the nip on the respective working rolls. Thus the bendability of the small-diameter working rolls is largely canceled out by the rigidity of the larger-diameter backup rolls so that the large forces required for rolling can be brought to bear on the workpiece.
To minimize roll bending and thereby improve the uniformity of workpiece thickness while also minimizing wear to the working rolls, it is known to make these working rolls axially shiftable. Thus as described in U.S. Pat. No. 4,669,296 it is known for the roll stand to have working-roll journal blocks which can be axially shifted in the frame with the respective working rolls, and to be able to bend the working rolls positively and negatively, that is respectively convex and concave toward the workpiece, a system also seen in U.S. Pat. No. 3,857,268. A pair of large-diameter and substantially parallel backup rolls flank and bear toward the nip on the working rolls. Respective journal blocks support the backup rolls in the frame for rotation about substantially parallel axes flanking and generally coplanar with the working-roll axes. A strip is passed repeatedly in a multipass run through the nip generally perpendicular to the plane while the working rolls are pressed against the workpiece to reduce its thickness. The working rolls are axially displaced relative to the workpiece a plurality of times during the run to change the region of contact between the workpiece edges and the working rolls during the run. The working rolls are also bent at least to maintain the workpiece thickness downstream of the nip generally uniform.
In such systems it is standard to simply provide a large double-acting hydraulic ram for each working roll. Since the workpiece is invariably centered in the rolling line, it therefore is necessary to move the two working rolls axially oppositely, so as either to decrease or increase the region of axial overlap while keeping the center of this overlap region in the same axial position. Such equipment is fairly complicated and bulky. It requires some monitoring to ensure that the axial opposite motion is indeed perfectly opposite and complementary, and when benders which cannot move relative to the respective rolls are provided the complexity is even increased.
Another problem is created in the systems where the working rolls are replaceable. In these arrangements the journal blocks of the working rolls are connected via appropriate formations such as described in German patent document No. 3,331,055 to pushers which are in turn connected to the respective axial-shifting actuators. This makes it fairly easy to disconnect a subassembly comprised of a working roll and its journal blocks from its respective pushers and replace it with a freshly ground one by releasing the journal blocks from the respective pushers and pulling them with the respective working rolls axially out of the service side of the stand. Nonetheless the provision of big individual actuators for the working rolls substantially complicated such exchange of working rolls.